Servovalve construction



April 8, 1969 J. L.. coAKLx-:Y ET Al.

SERVOVALVE CONSTRUCTION Filed March 1. 196e MIL April s, 1969 J. L.COAKLEY ET AL 3,437,101

sERvovALvE CONSTRUCTION Filed March 1, 1966 INV TORJ United StatesPatent O 3,437,101 SERVOVALVE CNSTRUCTIN James L. Coakley and Charles A.Kubilos, Gxnard, Calif., assgnors to Abex Corporation, a corporation ofDelaware Filed Mar. 1, 1966, Ser. No. 530,916 Int. Cl. F151) 9/03, 9/07,9/12 U.S. Cl. 137-83 17 Claims ABSTRACT F THE DISCLOSURE This inventionrelates to servomechanisms and more particularly to force feedbackoperated Servovalves.

Servovalves of the general type to which this invention relates areoperated by a torque motor and include two force amplification stages.Application of an electrical input control signal to an electromagnetcoil in the torque motor causes an unbalanced flux distribution in theair gaps around the motor armature, causing a torque to act on thearmature. The armature rotates in response to this torque, againstspring means which bias the armature to its centered or null position.Movement of the armature shifts a jet of fluid issuing from a jet tubefrom a null position in which it is centered between two receiver ports,to a new position in which the jet impinges unequally on the two ports.This deflection of the jet establishes a differential pressure betweenthe receiver ports which is proportional to the input current. The fluidemployed in conjunction with the jet tube may, of course, be eitherhydraulic or pneumatic iiuid. In the description to follow, it isassumed that hydraulic fluid is utilized.

The pressure in the receiver ports are fed to the second stage of theservovalve, which is a spool valve hydraulic force amplifier. Thedifferential pressure input from the first stage is reflected on opposedsurfaces of a main spool or piston in the second stage, shifting thespool and establishing communication between various ports. Flow throughthese ports in the second stage varies with spool position. Spoolmovement in response to the differential pressure continues until afeedback spring member, through which the spool and jet tube arecoupled, becomes suciently stressed that it returns the jet to the nullposition, thereby removing the pressure differential on the spool. Whenthis has occurred the spool thereafter remains in that position,controlling flow through the second stage `at a rate and directioncorresponding to the magnitude and polarity of the electrical inputsignal to the torque motor.

From an economic standpoint as well as from a performance standpoint,the Servovalves of the prior art have not been entirely satisfactory.The dissatisfaction can be traced to a number of structural featureswhich, because of theirdesign, have introduced complexities into themanufacture and assembly of the various component parts constituting thevalve. These complexities, in addition to increasing the costs ofmanufacture and assembly, have inherently limited the performance of theearlier valves.

For example, in one type of prior art servovalve the ICC spring meansused to bias the torque motor armature and jet tube to their balanced,central or null positions has included a tubular element which surroundsthe jet tube and which functions in bending as a spring when thearmature and jet tube are moved from their null positions.

In such valves, the spring means bends as the armature rotates inresponse to a signal. The extent to which the spring means bends isproportional to the total spring constant, which in turn is a functionof spring shape and thickness. Since predictable and reliable operationrequires close control of the spring constant, it has been foundnecessary in practice to machine these items with precision in order toaccurately regulate their characteristic, and, hence, their springrates. This need for precision machining has obviously added to the costof such servovalves.

It has been an objective of this invention to provide an improvedservovalve torque motor having an armature supporting and biasing springwhich is more eihcient of less critical manufacture, and which also ismore economical than those which previous torque motors have used.

A lfurther disadvantage of previous valves of the general type describedis they have not readily lent themselves to room temperature assemblyprocedures such as swaging, crimping, etc. Soldering or brazing hasusually been required to make the critical connections, which invariablyrequires more skill, is costlier, and tends to produce warpage which mayadversely affect valve operation unless compensated.

It has been a further object of this invention to provide a servovalveconstruction which eliminates the need for soldered or brazed connectionat critical points, thereby eliminating warpage and misalignnient whichmight otherwise be caused by heating of component parts during assembly.

Moreover, the prior art Servovalves have often been diflicult toassemble and align or adjust for maximum operating efficiency `andperformance. One assembled, they have been difficult to disassemble forcleaning, repair, and inspection purposes.

It has been an additional object of this invention to provide aservovalve which can be assembled and disassembled relatively easily,and in which the first and second stages are separate subassemblies.

It has been another object of this invention to provide interlockingpole piece mounting means for a servovalve which permit accurate air gapdimensioning during assembly and protect against pole piece positionalshifts while in use.

In a preferred embodiment of the invention, the torque motor armaturehas a pair of arms or wings on either side of a transversely extendinghollow central body. An elongated armature restoring element in the formof a thin walled tube extends through the interior lof the hollowcentral body of the armature. This tube is connected to and supports thearmature only at a point forward of the wings, and is connected to asupporting base only at a point on the rear side of the wings. A shaftor driver also extends through the armature, internally of the armaturerestoring tube, and is connected to the armature and tube only at thefront end thereof. Electromagnet coils are disposed on opposite sides ofthe armature and when energized are operative to turn the armature aboutthe common axis of the shaft and tube, thereby rotating the shaft. Theshaft or driver moves an elongated liexible jet tube which passesperpendicularly through an enlarged aperture in the rear portion of thedriver. The jet tube is secured at its fluid inlet end to the body abovethe -driver and is connected to the driver through an elongated tubewhich vsurrounds the jet tube and which is clamped to the jet tubeadjacent the fluid outlet end or nozzle thereof.

Use of the thin-walled tube described in this co-nstruction provides anumber of advantages: a single length of precision tubing serves jointlyas the support means for the armature, as a torsion spring biasing thearmature to null position, and as an isolation element for preventingoperating fluid within the hydraulic portion of the valve from reachingthe inside of the electrical portion of the torque motor. In addition,the configuration of the hollow tube herein provided permits it to beconnected toI the armature and supporting base by swaging techniques,thus avoiding the usual disadvantages of machining and warping due tosoldering or brazing during assembly.

In the torque motor, a pair of opposed, nonmagnetic members mechanicallyengage reference surfaces on the pole pieces of the electromagneticcoils and provide spacing means for establishing the proper air gapdimensions during assembly.

These anld other objects and advantages of the present invention will bemore readily apparent from a consideration of the following detailed'description of the drawings illustrating a preferred embodiment of theinvention.

In the drawings:

FIGURE 1 is a vertical section of a preferred embodiment of theservovalve of this invention, and is taken along the axis of the torquemotor.

FIGURE 2 is a longitudinal section taken along line 2-2 of FIGURE 1, andalso illustrates a typical hydraulic system including the servovalve.

FIGURE 3 is an enlarged vertical axial `section of the iirst stage ofthe valve, showing the details of the torque tube, armature, hyldraulicjet tube and receiver, and the force feedback spring assembly.

FIGURE 4 is a section taken along line 4-4 of FIG- URE 3.

FIGURE 5 is a partially exploded perspective View of the torque motorassembly.

FIGURE 6 is an enlarged View in perspective of the armature.

FIGURE 7 is a side elevation of the assembled torque motor.

FIGURE S is an enlarged view in section of a portion of the jet tube andreceiver.

The servovalve of this invention includes three principal sections,namely, a torque motor 1, a first force amplifying stage 2, and a secondforce amplifying stage 3. As best shown in FIGURES 1 and 2, in apreferred embodiment, the torque motor 1 and first amplifying stage 2are supported by la common base or frame member 4. Base 4 isnonmagnetic, and is mounted on a boldy 5, the body 5 also serving as acasing for the second section 3 of the servovalve. A housing 6 mountedon a horizontally extending fiange 7 of the body 5 encloses motor 1 andampliier 2.

The torque motor 1, as shown more particularly in FIGURES 5-7, includesa permanent magnet 8 having an upper north pole 9 and a lower south pole10. Magnet S may be an alnico permanent magnet. Sandwiched betweenmagnet 8 and' base 4 are opposed ferromagnetic upper and lower C-shapedpole pieces 11 and 12, respectively. The opposed planar end surfaces 13,14 and 15, 116 of pole pieces 11 and 12, respectively, are spaced,forming air gaps 17 and 18, respectively (see FIGURE 2). The permanentmagnet 8 functions to establish a urn'- directional magnetic flux ineach of the air gaps 17, 18.

Also sandwiched between magnet 8 and base 4 are a pair lof nonmagneticspacer members 19 and 20. Since members 19 and 20 are similar, only theleft member 19 will be described. Member 19 is C-shaped, as viewed fromabove, and includes opposed internal pole piece engaging surfaces 21, 22separated by pole piece end-engaging surface 23. Surface 22 is generallyplanar for engaging the back surfaces (adjacent base 4) of the .polepieces 11 and 12 to align them in its plane. Po-le piece-end-engagingsurface 23 is provided with a horizontal slot 25, and from this slothorizontal grooves 24 extend across the inner 4 side faces of the spacerto permit the assembly to be placed over the armature. The surface 23abuts the ends of pole pieces 11 and 12, establishing alignment in itsplane. The angulated internal surfaces 21, 21 (See FIG- URE 5) engagethe opposed beveled corner surfaces 26, 26 of the pole pieces 11, 12 andjointly function to locate and accurately space pole piece end `surfaces13, 14, thereby dimensioning air gap 17. Thus, when spacer 19 is snugly.fitted over the left ends of pole pieces 11 and 12, pole piece surfaces13 and 14 are horizontally and vertically aligned by surfaces 22 and 23,as well vas spaced apart to form an air gap 17 by angulated surfaces 21,21. Those skilled in the art will recognize the criticality of accurateair gap dimensioning.

A `forwardly extending, vertical ange 27 is formed on the roundedexternal surface 28 of each spacing member. Flange 27 is provided with aat shoulder surface 29, best shown on the spacing member 20 in FIGURE 5,and engages and seats in the internal end surface 30 of the magnet 8,thereby preventing movement of the spacing member relative to polepieces 11, 12 when the motor 1 is assembled.

The motor 1 also includes a pair of coils 31, 32 through the opencenters of which extend the flat Wings 33, 34, respectively, of anarmature 35 desecribed in detail hereinafter. In the assembled torquemotor 1, the coils 31, 32 are mounted by and between the opposed concavemagnet surface 30 and concave base surface 30a, pole pieces 11, 12, andspacing members 19, 20. The coil leads 36 pass through slots 37 in thespacing `members 19, 20 for connection to a suitable electrical signalinput means (not shown) which may be conventional.

The various parts of the torque motor assembly are held in operativerelation by two screws 38 and a plate 39. The screws 38 passsuccessively through plate apertures 40, magnet aperture 41, grooves 42in pole pieces 11, 12, and thence into tapped holes 43 in base 4. Asscrews 38 are tightened, magnet 8 and base 4 are drawn together,gripping the pole pieces 11, 12 and holding the spacing members 19, 20between them. The spaces between members 19, 20 and faces 30, 30a arelled with an epoxy which provides a positive interlock in the torquemotor.

The operation of the torque motor 1 follows principles which are wellknown and need not be discussed in detail. It is sufficient for thepurposes of understanding the various features of this invention toappreciate merely that a differential current applied to coils 31, 32will result in a magnetic torque being applied to ferromagnetic armature35, rotating it about its axis 44. Armature 35 rotates under the forceof the applied torque to an angular position within air gaps 17, 18Where the applied torque equals the armature restoring torque producedby means to be described. The direction and magnitude of the appliedtorque is dependent upon the level and polarity of the differentialcurrent owing in the coils 31, 32. For a detailed discussion of theoperation of torque motors, reference may be had to U.S. Patent2,891,181, to Raymond D. Atchley, issued June 16, 1959, and entitledTorque Motor.

The armature 35 of motor 1 is generally T-shaped as viewed in plan, andincludes a central tubular portion 5t) provided with oppoistelyextending flat wings 33, 34 of equal length (see FIGURE 6). Thedimensioning of wings 33, 34 is such that they extend into air gaps 17,18 respectively. Clearance is provided between the wings 33, 34 and thepole piece end surfaces 13, 14 and 15, 16 respectively, permitting thearmature 35 to rotate about its axis 44 in response to the applicationof an electrical signal to the windings 31, 32. The extent of armaturerotation is selectively limited by adjusting screws 51, 51 threaded intotapped holes in upper pole piece 11 (see FIGURE 2).

The forward extremity of central tubular portion 5t) of armature 35 hasa reduced internal diameter resulting in a stepped-diameter bore havinga small diameter bore section 52 and a large diameter bore section 53separated by an internal shoulder. Positioned within the bore sections52, 53 is a non-magnetic stepped-diameter armature-'supporting torqueand isolation tube 54. The torque tube 54 is secured at its reduceddiameter front end portion 55 to the end 57 of the armature tubularportion 50, and at its other end 56 to the base 4. The portion of tube54 intermediate ends 55 and 56 is coextensive lengthwise with boresection 53 of central armature portion 50, but is of reduced diameterand does not contact the armature.

The end 55 of torque tube 54 fits snugly within bore section 52 of thecentral armature portion 50 and is secured in place by an internallytapered swaging ferrule `60 which is pressed ove-r the externallytapered armature end 57. The complementary tapers of armature end 57 andferrule 60 securely lock the armature 35 and torque tube 54 to the endof a coaxial driver 65, providing a solderless connection therebetween.

The tube 54 at its inner end 56 is flared and fits snugly into a taperedbore 61 in base 4. An externally tapered swaging ferrule 62 pressedwithin flared end 56 of torque tube 54 secures the torque tube to base4. The complementary tapers of swaging ferrule 62 and base bore 61 lockthe flared end 56 of torque tube 54, thereby providing a solderlessconnection between the base 4 and the torque tube 54.

Thus, armature is supported within motor 1, with its wings 33, 34centrally poistioned within air gaps 17, 18 and biased against rotationabout its axis 44 by torque tube 54, the latter being connected at itsouter end to the front end of the armature and at its inner end, beyondthe opposite end of the armature, to base 4 via ferrules and 62,respectively.

The relation of the torque tube 54 and armature 35, as herein described,wherein the tube passes axially through the armature and is connected atits outer end to the armature enables a relatively long torque tube 54to be employed as the spring element in the torque motor 1. With a longtorque tube 54 in contrast to a short one, there is less angularrotation of the tube per unit length for a given armature rotation.

To transmit the torque output of motor 1 to the first amplifying stage2, a deflection or coupling means is provided. The coupling meansincludes a non-magnetic driver 65 which passes axially through torquetube 54. As previously mentioned, the outer end of driver 65 is securedto the armature 35 and torque tube 54 by swaging ferrule 60. At itsother or inner end driver 65 is secured through an element 66 having anopening extending therethrough at right angles to the driver, to an armor yoke 67 for movement therewith. Arm 67 has a right angle bendintermediate its ends, thereby forming an L-shape, and its lower portionthus projects forwardly beneath element 66 and parallel to driver 65.The connection between the vertical leg 73 of arm 67 and element 66 isby a screw 68 which passes through an oversized hole 69 in leg 73 andwhich is threaded into a tapped hole 70 in element 66. Radial teeth 71formed on the element face (see FIG- URE 4) engage the forward surface72 of vertical leg 73 to prevent relaitve angular movement betweencollar 66 and arm 67 when screw 68 is tightened.

The lower or forwardly extending leg 74 of arm 67 is provided with twoholes 75 and 76. A tube 77 is secured in hole 76 by suitable means.Soldering or brazing may be employed here since warpage is not criticalat this point. The lower end of tube 77, including the reduceddiameterlower end portion thereof, has circumferentiallyspaced longitudinalslots 78 therein. The slots 78 enable the reduced-diameter portion oftube 77 to secu-rely embrace the periphery of a vertically disposedflexible jet tube 85. This tube extends through and is gripped by thelower end portion of tube 77 under the action of a press fitted ring 80which clamps the slotted, reduced-diameter end portion of tube 77 to jettube 85.

In the first amplifying stage 2, jet tube extends through tube 77, hole76, and element 66 and is secured at its upper end only to base 4 by aconical-ended retainer plug `86 and screw 84. Plug 86 and screw 84cooperate with the sloping walls 87 of a threaded hole 88 to securelylock the flared end 89 of jet tube 85 relative to base 4 when screw 84is tightened. At its lower end, jet tube 85 is fitted internally with aprojector jet 90 having an outlet nozzle and which is secured in placeby a crimp 91.

The first amplifying stage 2 also includes a receiver 92. Receiver 92 isa plug having a pair of fluid passages 93, 94 (see FIGURE 8) which meetover a central knife edge 95. Passages 93, 94 communicate ywith passages96, 97, respectively, formed in a receiver supporting member 98. Thepassages 96, 97 in turn communicate with passages 99, 100 (see FIGURE 2)which constitute the inputs to the second amplifying stage 3.

The receiver supporting mem-ber 98 is connected to base 4 by means notshown and, when the servovalve is assembled, is positioned within acavity 101 in body 5, seating and sealing on surface 102 thereof. Apassage 103 is formed in member 98 which connects the upper end of jettube 85 to a source of pressure fluid via passage 104 in plug l86,passage 105 in base 4, passage 106 in body 5, filter 107, and inlet port108 in body 5.

In operation, when an electrical signal is applied to the torque motor1, armature 35 initially rotates from a centered position to a pointwhere the restoring force on the armature 35 equals the magnetic torqueproduced by the electrical input. These restoring forces arise fromdeflection of the torque tube 54, jet tube 85 and a feedback spring tobe described. The armature rotation is transmitted to the jet tube `85via driver 65, element 66, arm 67, and tube 77, bending or deflectingjet tube 85 from a centered position directly over knife edge 95 of thereceiver. As the jet tube 85 is deflected from the centered, nullposition shown in FIGURE 8, it directs a greater proportion of the fluidissuing from its nozzle 90 to one or the other of the receiver passages93, 94. The pressure in that receiver passage toward which the nozzle 90is deflected will increase while the pressure in the other passage willdecrease. Excess pilot llo-w from jet tube 85 which is not accepted byeither receiver passage flows to a fluid reservoir. Thus a differentialbetween the pressures in passages 93 and 94 is developed. Thisdifferential constitutes the input to the second amplifying stage. Aslight rotation of armature 35 produces a relatively large displacementof jet tube 85 and a relatively large pressure differential developsbetween passages 93 and 94. This pressure differential is capable ofdeveloping much larger forces than could be developed by the armaturealone. Hence, force multiplication is produced by the `first amplifyingstage.

The second amplifying stage -3 includes a main spool valve having aspool or piston 110 slidable in a bore 111 of a sleeve 112 (see FIGURE2). Spool 110 has a series of axially spaced peripheral grooves G1, G2,and G3. Sleeve 112 is fitted into a bore 113 in the body 5 and it isprovided with a plurality of port means P1, P2, P3, P4 and P5 whichcommunicate with bore 111 at axially spaced positions, and whichcooperate with spool grooves G1-G3 to direct the flow of fluid throughthe main valve. Ports P1-P5 can be interconnected in various ways by theselective positioning of spool 110 relative to sleeve 112. For example,if the spool valve is to control or meter the flow of fluid a variablespeed reversible motor M, motor ports M1 and M2 may be connected toports P2 and P4, respectively. The pump outlet port is connected to bothports P1 and P5, and port P3 is connected to a tank T. In such a system,when spool 110 is moved to the right in sleeve 112, the motor M isdriven in one direction by fluid from pump P lwhich takes the followingpath: port P1, lgroove G1, port P2, motor port M1, motor M, motor portM2, port P4, groove G2, port P3, to tank T. If spool 110 is moved to theleft, motor M is driven in the opposite direction by iluid from pump Ptaking the path through port P5, groove G3, port P4, motor port Mz,motor M, motor port M1, port P2, groove G2, port P3, to tank T. Thespeed at which motor M is driven depends, of course, on the ow ratethrough motor M, which in turn depends on the extent to which spool 110is displaced from the centered position wherein no flow occurs.

The port P3 in sleeve 112 also communicates with the region surroundingprojector jet 90, thereby providing a path to tank T for excess jetstream fluid not entering either of the two receiver ports 93, 94.

The means for selectively moving spool 110 includes pressure chambers115 and 116 in bore 111, pressure in which acts upon the opposite endsurfaces of spool 110. Chambers 115 and 116 communicate with passages99, 96, 93 and 100, 97, 94 respectively, and reect the differentialestablished by the lirst stage. Adjustable stops 117 and 118 are sealedto bore 111 and can be positioned axially therein to limit the movementof spool 110 by plugs 119 and 120` respectively which are threaded intobody 5.

In operation, the input to the second amplifier stage 3, that is, thepressure differential between passages 93, 94, produces a differentialor net axial force on spool 110. The direction which this diiferentialforce moves spool 110 depends upon the polarity ofthe electrical signalinput to the motor 1. Thus, fluid ows to motor M, in the selecteddirection.

Since the electrical signal is supplied for as long as it is desired todrive motor M, which usually will be much longer than it takes spool1111 to shift an amount corresponding to the ow rate and motor speeddesired, force feedback means are provided. This force feedback meansincludes a feedback spring 125 which is connected at its upper end 126to horizontal leg 74 of arm 67. The connection is effected by securingend 126 in hole 75. The other end 127 of spring 125 has a ball 12Sattached thereto. Ball 128 fits accurately and without play in a crossbore 129 in spool 110 forming a cam connection between the spool and thefeedback spring.

Spool 110 will move in sleeve 112 as long as there is a pressuredifferential between chambers 115 and 116. Since this pressuredifferential is caused by the unequal impingement of iluid on receivers93, 94 due to the deection of jet tube 85, the force on spool 110 willremain as long as the jet pipe 85 is deflected. However, spring 125 isresponsive to the position of spool 110, and supplies a feedback forceto driver 65 which returns jet tube 85 to null position and therebyremoves any net force on the spool 110 when the spool has been shiftedan amount corresponding to the magnitude of the input signal.

By way of example, referring to FIGURE 2, a counterclockwise jet tuberotation will produce an unbalanced force in chamber 116 which shiftsspool 110 to the left. As spool 110 moves to the left, it rotates thefeedback spring 125 clockwise. This clockwise motion is transmitted toarm 67, which in turn transmits it to the armature and tends to turn thejet tube clockwise to the null position. The spool position at whichfeedback spring 125 returns jet tube 85 to the null position correspondsto a unique and discrete input current level. Hence the servovalve willregulate the speed of motor M in accordance with the input signal. Thespool 110 will remain in this position until the electrical signal isagain varied.

It will be apparent from the symmetry of the valve that oppositely poledelectrical input signals rotate the armature 35 and torque tube in theopposite direction, causing the spool to move toward the other side ofits center or neutral position.

From the foregoing it will be apparent that the interrelation of thearmature, torque tube, driver, arm, jet tube, and force feedback springprovides an assembly which is exceedingly compact in relation to thehigh gain which can be attained. The torsion spring length is relativelylarge in proportion tothe small size of the assembly, as shown in FIGURE3. Moreover, the arrangement of the rst stage elements wherein the jetpipe projects through the driver and is engaged by the outer tube 77only adjacent its lower end, provides a relatively long lever arm incompact form. Assembly of the valve is facilitated since the entire rststage subassembly forms an integral unit with torque motor 1 which canbe tted as a unit to the second stage 3.

While we have described a preferred form of this invention, it will beunderstood that it is susceptible of various modications andadaptations.

We claim:

1. Apparatus comprising:

a base;

a torque motor mounted by said base; said motor including an armaturehaving an axis of rotation and an axially disposed central tubularportion;

torsion spring means mounting said armature to said base for torsionallyconstrained rotational motion about said axis of rotation, said torsionspring means comprising a torque tube which is connected at one end tosaid armature, said torque tube extending through said tubular portionof said armature and being connected at its other end to said base;

a flexible jet tube having a fluid inlet end and a uid outlet end, saidfluid inlet end being secured to said base, said jet tube extendingangularly with respect to said axis;

motion transmitting means connecting said armature and said jet tube fordeflecting said jet tube in accordance with the rotation of saidarmature, said motion transmitting means extending angularly from saidaxis and comprising,

a driver extending axially through said torque tube and connected tosaid armature for rotational movement therewith, and coupling meansextending at an angle to said axis of rotation and connecting saiddriver and said jet tube for angularly deliecting the uid outlet end ofsaid jet tube in accordance with the rotation of said armature,

said jet tube being secured to said base above said driver and extendingfreely through an aperture provided in said driver,

and further wherein said coupling means is connected to said jet tubebelow said driver.

2. Apparatus comprising:

a base;

a torque motor mounted by said base; said motor including an armaturehaving an axis of rotation and an axially disposed central tubularportion;

torsion spring means mounting said armature to said base for torsionallyconstrained rotational motion about said axis of rotation, said torsionspring means comprising a torque tube which is connected at one end tosaid armature, said torque tube extending through said tubular portionof said armature and being connected at its other end to said base;

a flexible jet tube having a iluid inlet end and a fluid outlet end,said fluid inlet end being secured to said base, said jet tube extendingangularly with respect to said axis;

motion transmitting means connecting said armature and said jet tube fordeiiecting said jet tube in accordance with the rotation of saidarmature, said motion transmitting means extending angularly from saidaxis and comprising,

a driver extending axially through said torque tube and connected tosaid armature for rotational movement therewith, and coupling meansextending at an angle to said axis of rotation and connecting saiddriver and said jet tube for angularly detiecting the fluid outlet endof said jet tube in accordance with the rotation of said armature,

said coupling means including a tubular clamp member through which atleast a portion of said jet tube extends, said tubular clamp member atone end being connected to said driver, the internal wall of said clampmember being spaced over most of its length from said jet tube, saidtubular clamp member at the other end thereof being connected to saidjet tube adjacent said iiuid outlet end thereof.

3. The apparatus of claim 2 wherein said driver is connected to saidarmature through said torque tube at said one end thereof, and furtherwherein said coupling means also includes a generally L-shaped armconnected at one en-d to said driver and having a leg extending parallelto said driver, said jet tube passing freely through an aperture in saidleg, said clamp member being secured to said leg.

4. The apparatus of claim 3 which further includes an elongated forcefeedback spring extending downwardly from said leg.

5. The apparatus of claim 2 wherein said jet tube is clamped to saidbase and said tubular clamp member is clamped to said jet tube, withoutthe necessity of brazing.

6. Apparatus comprising:

a shaft rotatable about an axis in response to a signal;

a base;

a flexible jet tube angularly disposed relative to said shaft and whichintersects the axis of said shaft, said jet tube having a liuid inletend xed relative to said base, said jet tube also having a iluid outletend; and

motion transmitting means angularly disposed relative to said shaft,said motion transmitting means being connected between said jet tube ata point intermediate said ends and said shaft for arcuately moving saidlluid outlet end in a plane intersecting the axis of said shaft at anangle thereto.

7. Apparatus comprising:

a base;

a torque motor for angularly positioning rotatable means in response toan electrical input;

a exible jet tube having a fluid inlet end mounted to said base, saidjet tube also having a iiuid outlet end, said tube between said inletand outlet ends extending through an enlarged opening provided in saidrotatable means, said jet tube being spaced from said rotatable means insaid opening; and

a tubular clamp member through which at least a portion of said jet tube`freely extends, said tubular clamp member at one end being connected tosaid rotatable means for rotation therewith, said tubular clamp memberat the other end thereof being connected to said jet tube adjacent saidiiuid outlet end thereof.

8. The apparatus of claim 7 wherein said rotatable means comprises agenerally cylindrical driver and an L- shaped portion projectinggenerally perpendicularly to said driver, said L-shaped portion having aleg extending substantially parallel to said driver, said driver and legboth having apertures therein through which said jet tube freelyextends, said clamp member being secured at said one end thereof withinsaid aperture of said leg and projecting away from said driver.

9. Apparatus for amplifying an input signal applied as a torque actingon a shaft, said apparatus comprising:

a frame member;

a flexible jet tube having a fluid inlet end cantilevered to said framemember and having a jet outlet at the other end thereof;

a receiver having two adjacent receiver ports, said receiver beingmounted to said frame member, said jet outlet being positioned to directuid issuing therefrom to impinge on said receiver ports;

a substantially tubular clamp member within which at least a portion ofsaid jet tube is positioned, said tubular clamp member at one endloosely encircling an intermediate portion of said jet tube between theends of said jet tube, said clamp member at said one end being connectedto said shaft, said tubular clamp member at the other end thereof beingconnected to said jet tube between said jet outlet and said intermediateportion, dellection of said jet tube by said clamp member in response torotation of said shaft in operation developing a pressure differentialbetween said receiver ports;

a body;

a spool valve including a bore in said body and a spool slidable withinsaid bore for varying the iiow of fluid through said valve;

two passages formed in said body and communicating, respectively, witheach of said receiver ports; and

force feedback means operatively connected between said spool and saidjet tube for centering said jet outlet between said receiver ports whensaid spool advances to a position correlated with the input signal.

10. The apparatus of claim 9 wherein said force feedback means includesa spring element having lirst and second ends, said tirst end beingconnected to said jet tube through said clamp member, and said secondend including a cam follower in sliding contact with a cam surfaceformed by said spool for imparting pivotal motion to said spring elementin response to sliding movement of said spool.

11. The apparatus of claim 9 wherein said shaft is operated by a torquemotor.

12. The apparatus of claim 9 further comprising:

a torque motor mounted on said frame member; said motor including anarmature having an axis of rotation and having an axially disposedtubular portion; torsion spring means mounting said armature to saidIframe member for torsionally constrained rotational motion about saidaxis, said torsion spring means comprising a torque tube positionedwithin said tubular portion of said armature and connected at axiallyspaced points to said torque tube and said frame member, and furtherwherein said shaft comprises a member concentric with said torque tubeand connected to said armature for rotational movement therewith.

13. The apparatus of claim 9 further comprising:

a torque motor including magnetic circuit means mounted on said framemember, said magnetic circuit means having spaced poles defining an airgap, said spaced poles having reference surfaces thereon; a spacingmember enclosing at least a portion of said pole pieces, said spacingmember having geometrically spaced means for engaging said referencesurfaces for establishing and maintaining a predesigned air gap; anarmature having an axially disposed tubular portion; a torque tubepositioned within said tubular portion and connecting said armature andsaid frame member for torsionally constraining rotational motion of saidarmature; and wherein said shaft comprises a driver concentric with saidtorque tube and connected to said armature for rotational movementtherewith.

14. Apparatus comprising:

a base;

a torque motor mounted by said base; said motor including an armaturehaving an axis of rotation and an axially disposed central tubularportion;

torsion spring means mounting said armature to said base for torsionallyconstrained rotational motion about said axis of rotation, said torsionspring means comprising a torque tube which is connected at one end tosaid armature, said torque tube extending through said tubular portionof said armature and being connected at its other end to said base;

a tiexible jet tube having a uid inlet end and a fluid outlet end, saiduid inlet end being secured t-o said base, said jet tube extendingangularly with respect to said axis;

motion transmitting means connecting said armature and said jet tube fordeecting said jet tube in accordance with the rotation of said armature,said motion transmitting means extending angularly from said axis andcomprising,

a driver extending axially through said torque tube and connected tosaid armature for rotational movement therewith, and coupling meansextending at an angle to said axis of rotation and connecting saiddriver and said jet tube for angularly deecting the uid outlet end ofsaid jet tube in accordance with the rotation of said armature,

said armature, torque tube, and driver being secured together by aswaging ferrule around a tapered surface provided on said armature.

15. Jet tube servovalve apparatus comprising:

a frame;

a torque tube rigidly mounted to said frame;

an armature;

means rigidly connecting said armature to said tube at a position onsaid tube spaced from the rigid mounting of said tube to said frame;

magnetic means tending to rotate said armature about the axis of saidtube;

a flexible jet pipe having a fluid outlet end;

means fixedly securing said jet pipe to said frame at a position spacedfrom said outlet end;

conduit means for supplying pressure fluid into said jet pipe;

t-ube means surrounding and connected at one end to the jet pipe, saidtube means having a free end sur- 30 rounding said jet pipe; meansresponsive to rotational movement of said armature about said axis andconnected to the free end of said tube means, to deflect the outlet endof said jet pipe relative to the position at which the jet pipe is xedlysecured to the frame,

a feedback spring connected to said free end of said tube means,

and receiver port means for said jet pipe, said receiver port meansbeing xedly positioned with respect to said frame.

16. The apparatus of claim 15 wherein a shaft extends through saidtorque tube and is connected for rotational movement with said armature;and

coupling means are connected between said shaft and said `jet pipe, saidcoupling means extending at an angle to said axis and angularlydefiecting the fluid outlet end of said jet pipe in accordance with therotation of said armature.

17. The apparatus of claim 16 in which said jet pipe is a normallystraight tube having a uid inlet at one end thereof remote from saidoutlet end, said inlet being xedly connected to said frame,

ALAN COI-IAN, Pri-mary Examiner.

U.S. Cl. XR.

